Z Code for Power Press Operation: Health, Safety, and Guarding Requirements

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1 Z Code for Power Press Operation: Health, Safety, and Guarding Requirements Scope Released in December 2002 occupational health and safety requirements for all classes of power presses that are fitted with a ram (plunger or slide) and dies for the purpose of blanking, cutting, trimming, drawing,punching, forming (bending), stamping, assembling, or processing metal and other materials. 1

2 Section 1.3 It is recommended that a schedule be developed d and implemented that t will ensure compliance with all applicable parts of this Standard no later than 2 years from the date of its publication. This should all be done since the deadline was January 05 Circuit Performance Cycle Initiation and Safety circuits shall hllbe control reliable libl Electric, Hydraulic, Pneumatic, & Muting Circuits 2

3 Control Reliable Control reliable safety control systems shall be dual channel with monitoring, and Designed, constructed and applied such that any single component failure Including monitoring shall not prevent the stopping action of the press. Safety Circuit Performance The monitoring shall generate a stop if a fault is detected. A warning shall be provided if a hazard remains after cessation of motion; 3

4 Safety Circuit Performance These safety control circuits shall be independent of the normal program control circuit and shall not be bypassed or removed without t being detected. t d The single fault should be detected at time of failure. If not practicable, the failure shall be detected at the next demand upon the safety function. This would include press initiation control circuits, trip control circuits or other elements of the control system which affect the protection from point of operation hazards. Safety Circuit Performance Safety circuits shall be control reliable Electric this includes electrical interlocks for safety gates Clutch/brake control system Emergency stops Presence sensing devices 4

5 Safety Circuit Performance Safety circuits shall be control reliable Hydraulic this includes Hydraulic interlocks for safety gates Valve systems On hydraulic clutch/brakes On single or dual cylinder down acting hydraulic presses Including secondary restraint devices Safety Circuit Performance Safety circuits shall be control reliable Pneumatic this includes Pneumatic interlocks for safety gates Valve systems On pneumatic clutch/brakes On single or dual cylinder down acting pneumatic presses Including secondary restraint devices 5

6 Cycle Initiation Press cycle initiation circuits shall be control reliable and: be protected against the possibility of an accidental ground causing the press to operate; prevent guard muting unless the press main motor is energized in the forward direction; (mechanical presses) Only allow inch mode when operating in the reverse direction prevent the initiation of a press stroke should the main motor(s) be energized after the clutch has been engaged with the flywheel at rest. Not allow guard muting during any hazardous portion of the cycle/stroke.and have controls that automatically stop the press when the power to the press initiation circuit is stopped or fails. The restoration of power or normal supply shall not reactivate the cycle control until the tripping or start mechanism is operated. Interlocks or Monitoring Circuits Mechanical Presses Interlocks or monitoring circuits shall be provided to prevent or stop ram motion if power to a safeguarding device fails; the drive train for a rotating ti cam limit it switch, or ram position monitoring device becomes loose, breaks, fails ; or a press safety valve fails. Hydraulic and Pneumatic Presses Interlocks or monitoring circuits shall be provided to prevent or stop ram motion if power to a safeguarding device fails; or a dynamically monitored valve fails. All components and subsystems of the control system shall be designed and constructed to operate together in order to provide total system compliance with the requirements of this Standard. 6

7 Brake monitor Part Revolution clutch h/b brake 72321Ai Air/Hydraulic All part-revolution presses utilizing air or hydraulic clutches shall be equipped with a press safety valve and a brake monitoring device. Brake monitor On mechanical presses equipped with spring-set brakes where the point of operation is protected by safeguarding devices that signal a stop, the press shall be equipped with a brake/stopping performance monitor that shall be; (a) designed, constructed, installed, and incorporated with the press control circuit to prevent the initiation of a successive stroke if there is an increase in the stopping time beyond the end user s predetermined limit; (b) constructed and installed in a manner to monitor brake system performance every time the brake is applied; and (c) capable of supervisory control for adjustment. 7

8 Counterbalance Systems Spring Counterbalance Air Counterbalance Hydraulic Counterbalance Spring Counterbalance System shall incorporate means to retain system parts in the event of breakage. shall have the capability of holding the slide and its attachments at midstroke, without the brake applied. 8

9 Air / Hydraulic Counterbalance System shall retain the piston and rod in case of breakage or loosening. shall hold the slide and its attachments at any point in the stroke without the brake applied. Information relating to attachment weights and proper counterbalance pressures shall be provided. In the case of an air supply failure For part revolution clutch-presses, the clutch is disengaged gg and the brake is applied. Reactivation of the clutch shall require restoration of normal air supply and the use of an initiation device. For full revolution presses Engagement of the clutch shall require restoration of normal air supply and use of the trip control mechanism. Typical Counter Balance System 9

10 Pneumatic Requirements A pressure switch shall be installed to stop the press if the air pressure is lost A lockout device shall be provided that shall be capable of being locked in the OFF position. shall be easy to operate (e.g., a simple pull/push action) have an exhaust port equal to or greater than it s supply line have a pressure indicator (ie: a gauge), that is visible to the operator to indicate that the line is bled. All mufflers shall have sufficient capacity so as not to restrict the exhausting of the system. Lubrication shall be provided for components requiring it. Dual Safety Valve A Press safety valves shall be installed on all presses with air or hydraulically operated clutches. Solenoids of the press safety valves shall be independently controlled. A cyclic check of pressure in both systems of the press safety valve shall be carried out if individual press safety valves for clutch and brake are used Some manufactures have jumpers installed that need to be removed to comply with the code 10

11 Hydraulic/Pneumatic Presses Hydraulic/pneumatic circuits used for press cycle initiation or any control that affects operator safety at the point of operation, shall be control reliable The operating pressure rating of all hydraulic components shall be equal to or greater than the maximum working pressure of the press. Examples of hydraulic components may include valves, accumulators, cylinders, regulators, fittings, pumps and piping. Over-pressure protection shall be provided to ensure that the maximum rated pressure of the press is not exceeded. Accumulators Means shall be provided to vent or isolate accumulator fluid pressure from causing unintended slide motion. When accumulators are used with flammable fluid systems, the accumulator shall be charged with inert gas. Bleed down to occur automatically when the system is shut down and shall be accomplished with a non-silting (sticking resistant) type valve. Relief valve protection. Bladders and seals shall be compatible with the fluid. A check valve shall be installed in pump outlet to avoid reverse driving of the pump at shut down. Include a gauge or test connection to check the pressure in accumulator. Caution should be taken to recognize that accumulators are pressure vessels and are pre-charged with an inert gas. Care shall be taken when performing maintenance or repair on these items. 11

12 Cylinders Means shall be provided to prevent pistons from creating a hazard from stroking outside it s design limits. Means shall be provided to prevent side loading on cylinder rods. Filtration Hydraulic/pneumatic fluid quality shall be maintained and monitored as required to meet the manufacturer s recommendations and thus minimize hazardous motion of the press. As a minimum, filters shall be equipped with a mechanical indicator that gives a visual indication of when the element(s) require replacement or cleaning. Temperature Control A means shall be used to maintain the fluid temperature level within the fluid specifications and the system s operating limits. This may require heating or cooling of the fluid. Excessive hydraulic fluid temperature may pose a hazard to personnel. Temperature must also be controlled within limits that are compatible with the fluid seals and components in the system. Pressure Intensification i The circuit design shall give due consideration to avoid hazardous effects of pressure intensification under all conditions. 12

13 Pressure Unloading When operator entry into the point of operation occurs, the design shall incorporate a valve element that ensures elimination of pressure buildup on the closing side the cylinder (ram). The elimination of pressure buildup shall occur with the valve in it s at-rest (de-energized) state and shall remain so in the event of an electrical power failure, and must be cyclically monitored at each press stroke. It is important that during this unloaded time the oil on the top of the ram(s) not be locked such as to prevent manual upward movement of the platen should such action become necessary. The circuitry must allow manual jacking of the platen, for example, to free a trapped person during a rescue operation. Decompression The circuit design shall be such as to provide a means of decompression in order to reduce or eliminate the detrimental effects of shock. Piping Each run of piping shall, be continuous from one piece of apparatus to another. Rigid piping shall be securely supported at frequent intervals to avoid vibration or movement. Where a drop in pressure could lead to unintended dangerous motion of the slide/ram, flexible piping shall not be used. Solid pipes and pipe connections shall be chosen to prevent such a loss of pressure. Where possible, holding valves and such devices should bolt direct to the actuators. Operating valves shall not depend on connected piping for support.. 13

14 Control Valves Control valves and other control components shall be mounted in positions, which provide accessibility and avoid damage. Where valves are manually or mechanically (as distinct from electrical) operated, the arrangements for restoring the valves shall be positive, i.e., when the actuator of the valve is released, the valve shall automatically move to the safe position. Controlled Gravity Descent Controlled gravity descent may be a deliberate design feature to facilitate rapid closing of the tools. In such a case, all the fluid in the cylinder supporting the slide/ram shall be passed through the main control valve(s). 14

15 Controlled Gravity Descent For down stroking presses, provisions shall be made to protect the cylinder and components from damage due to pressure intensifications. A relief valve used for this purpose shall be direct operated, sealed, and locked against unauthorized adjustment, and shall be set at a pressure at least 10% above the maximum pressure so that it only opens in the case of a fault. The components it protects shall be designed to sustain the pressure at which the valve is set. If a single break in the spring occurs the relief valve shall be constructed so that the space between the windings remains less than one wire thickness. The spring shall be guided so as to maintain the function of the relief valve. Unintended Gravity Fall Single Cylinder Systems Where there is a risk of injury, in addition to the main Tonnage Ram a minimum of one of the following shall be incorporated: a monitored mechanical restraint device, and/or a monitored hydraulic restraint device. The restraint devices shall operate automatically and shall be effective throughout all portions of the stroke/cycle during all times that the operators have access to the tools, pinch points, or danger zone. Each restraint device must be individually capable of holding the slide platen and tooling. 15

16 > Single Cylinder C/W Counter Balance System > Single Cylinder C/W Mechanical Restraint 16

17 Unintended Gravity Fall Multiple Cylinder Systems Where two cylinders are used to operate a slide/ram, both shall be independently attached and each controlled with a cyclically monitored valve capable of independently holding the slide/ram in the event of a mechanical or hydraulic/pneumatic failure of one. Load Holding During Non-Production Times Where there is a risk injury from a gravity fall or drift of the slide platen, a mechanical restraint device, for example, a safety blocking device, shall be provided to be inserted in the press for use during repair, or any necessary intervention between the tools at times other than normal manual feeding. Note: The risk of injury will not occur between the tools of an upstroking press, but can occur below the moving tool. Multiple Cylinders 17

18 Automatic Operation Presses utilizing closed tools, with fixed and interlocked enclosing guards where no access to the hazard area is possible, a single valve should be provided as a minimum in accordance with good design principles. These presses shall not be used where the operator is exposed to hazards in the point of operation. 4 way circuit The Double Valve controls the incoming oil and the release of pressure in the hazardous direction. Hazard direction 18

19 Example of self-monitoring hydraulic double valve 19

20 Who & Where Are We? Professional Electrical Engineers. Jim Van Kessel: 566 Fishermills Road Cambridge, Ont. N3C 2V ; Cell: ; Fax: Chris Gow: 925 Dublin Street Whitby, Ont. L1N 1Y ; Cell: