Information sheet for installing and troubleshooting Valve-Less Vacuum and Vent Blocks

Once you’ve decided to utilize the Valve-Less Vacuum or Vent Block several items are critical to successful implementation and use.

Midland Technologies provides the recommended block size after receiving a complete Valve-Less Vacuum/Vent Block Sizing form (or download). Midland will design the vacuum or vent block runner system upon the receipt of a PO for a set of blocks and a 2D dxf file of the tool layout.

There is no charge for this service. If a solid model of the part and gate-runner system is received a simulation will be run at no charge to determine the last places to fill.

Correct Vacuum or Vent Block installation are critical to proper function.

1. Pockets should be machined per the sizes available from Midland Technologies. Blocks should be pre-loaded to the same height as inserts.
2. Blocks are to be installed in the mold base if at all possible. Blocks must be inserted 4.50” in from the edge. If that is not possible, a support system for the blocks must be constructed to assure shut off. A sketch of this support system is available with the purchase of a vacuum or vent block.
3. Keys are provided in each block for assuring alignment between the halves. Proper machining of the pockets is critical to assure a good fit between the face of the blocks and the inserts. If pockets are not correctly machined to tolerance the key may not hold and shift in block could occur leading to shutoff of venting or vacuum.
4. Blocks should be installed up to the hardened insert steel or a vacuum runner block should be included in the design to ensure shut off.
5. Retrofitting vacuum blocks to existing tools requires special consideration of alignment of halves of the mold base. A check of the clearance between leader pins and bushings must be performed, and if not to original dimensions new pins and bushings are recommended to assure proper clearance in vacuum or vent blocks.
6. An ejection pin located in the main runner extension is required to assure removal of the vacuum runner. This pin should not be located in the vacuum block.
7. The vacuum runner should have sufficient turns before feeding into the main vacuum block runner; a minimum of 5 turns is recommended.
8. Vacuum gates are sized proportional to the block area.
9. Vacuum runners are to be designed to reduce metal velocity as they approach the main vacuum runner.
10. Water is provided in the blocks using the horizontal mounting holes. If water is used the vertical holes are to be used for retaining the blocks.
11. Locate vacuum gates at the last place to fill on the edge of the cavity.

The most prevalent problems associated with the vacuum block is poor runner design allowing metal to blow through the blocks, or improper installation leading to block shift.

Trouble shooting vacuum or vent blocks

Condition: Metal flashing through the Valve-Less Vacuum or Vent Block.

Possible causes:

1. Improper design of vacuum or vent block runners
2. Pre-load of block not sufficient to achieve shut off
3. Temperature of insert is higher than the block creating a gap
4. The block is too hot allowing metal to flow through
5. Tool flashing allowing metal to flow through
6. Excessive metal velocity in vacuum runner to the block
7. Damaged block

Solutions:

1. Design the vacuum runner with a minimum of 5 turns from the casting to the main block runner
2. Make sure the blocks are pre-loaded the same as the inserts and shim if necessary
3. Check temperature of inserts and blocks. Blocks may have to be shimmed to compensate for temperature difference.
4. Add cooling to block
5. Clean the tool to make sure the tool is shutting off properly, blow off parting line or use solder to check.
6. Check size of runners to ensure areas are increasing as you approach main block runner. All should not exceed main block runner.
7. Inspect block for damage, nicks, stuck pieces of metal, remove and repair block or replace. Midland can evaluate blocks for possible repairs.

Condition: Solder of teeth in block

Possible causes:

1. Excessive metal velocity
2. Damaged block
3. Improper design of vacuum or vent block runners

Solutions:

1. Check design for proper number of turns. Measure areas of runners to make sure areas are not exceeding main block runner.
2. Check block for damage due to closed up tool.
3. Review basic runner design

Condition: Low or no vacuum

To determine level of vacuum being pulled use gage attached to the die and pull vacuum through the block.

Possible causes:

1. Vacuum pump failure
2. Leaking vacuum system (hose, pipe, valve, filters and related components)
3. Plugged filter
4. Plugged vacuum hose or component
5. Pinched off vacuum block, no gap. (use solder strip in block and close die, measure thickness, if less than .020” block is improperly aligned)
6. Metal stuck in vacuum system (block or runner)
7. Die is not shut off due to excessive flashing

Solutions:

1. Check vacuum pump and gauge
2. Check for leaks on all components
3. Check and clean filter
4. Check and clean hoses and components
5. If gap is less than .020” correct block alignment. Block installation, keys, and die alignment should be corrected
6. Measure runner areas to adjust to correct size
7. Correct shut off problem same as any tool requires for eliminating flash. If retrofitting vacuum, make sure any pre-existing vents that were in the die  are welded off completely

Condition: Stuck metal in vacuum runner or block

Possible causes:

1. Lack of draft
2. Excessive metal velocity
3. Lack of ejection

Solutions:

1. Add draft to runner
2. Check areas of runners to make sure they are increasing as they approach the main vacuum block runner
3. Add ejector pins to the runners as required

Methods of checking vacuum

1. Glove over pour hole (cold chamber) make sure your hand is not in it. Close die, turn vacuum on, place a glove or rag over the cold chamber pour hole and observe if there is a pull from the vacuum
2. Make plug to fit cold chamber pour hole and mount vacuum gauge
3. Install mini block with a gauge in tool, cut a runner from block to overflow and use to read vacuum level (hot chamber and thixomolding)

Comment:

We do not recommend the use of seals in the tool due to high maintenance cost associated with their use. If the ingate metal feed system and the machine process are controlled along with a properly designed vacuum system there should be very few tools requiring seals.