Dummy Blocks - Castool Tooling Systems

Extrusion > Dummy Blocks

The dummy block is a critical element for extrusion quality and press performance. A dummy block is in direct contact with the billet. Therefore, its successful operation depends on several factors. The most important factor among them is its’ efficient interaction with a round, straight, thermally – and, therefore, dimensionally – stable container.

Bayonet Coupling

HPR, Marathon, and RRB

Castool uses a unique bayonet-type coupling which locks the dummy block quickly and securely to the stem. This makes it much easier and faster to replace a very hot block than with a conventional screw-type or rod coupling. Castool uses a secondary stabilizing stud (behind the bayonet), to limit the amount of lateral movement of the block on the stem. The stabilizing stud can reduce the lateral movement from 0.7 mm to 0.2 mm.

HPR – High pressure ring block, is an evolution of the old favorite QEB, quick expansion block. The HPR has a similar expanding wear component. The full-length ring is relatively thin and of uniform thickness. It expands quickly, making it suitable for presses with rapid acceleration. The ring has an interference fit with the body or holder, which allows the pad to be very large. The large pad area reduces high pressure deformation.

Marathon – This extra strong 2-piece block emphasizes quality of product plus length of operating life. The sturdy design provides excellent long elasticity life and rigidity.

RRB – Replaceable ring block for standard long stroke presses up to 100,000 psi. The combinations of the ring hoop strength and the yield strength of the mandrel and holder have been carefully designed. The ring expands to pre-determined size at a pre-determined pressure. It provides long-lasting dummy block elastic expansion and contraction.

Purpose

Allow gases to escape during the combined process of billet upset, and burp decompression, reducing blisters
Maintain a minimal uniform skin of aluminum on the liner inner diameter reducing profile inclusions

Function

The function of the dummy block is the extension of the ram or stem, which pushes the softened alloy through the die. There are a number of functions that must be satisfied by an effective dummy block.
To repeatedly transmit the force of the ram, at high temperature, to the alloy
To expand to pre-determined size under load and maintain a secure seal with the container wall, leaving only a thin film of alloy on the liner
To separate cleanly from the billet at the end of the stroke
To contract immediately, and return through the container without stripping the film of alloy from the liner
To cause no gas entrapment that can result in blistering, or damage the face of the container and/ or dummy block
To compensate for minor press misalignment
To be quickly and easily removed and replaced
To function effectively until a production run is complete

Benefits

Reduce scrap, due to back end blisters and surface defects
Reduce cost of operation
Reduce downtime
Increase productivity
Increase operating life
Increase container liner life

Superior Quality & Performance

BETTER CASTINGS & PROFILES FASTER

Castool’s expertise in material, manufacturing and temperature management enables us to design and manufacture specialty tooling for many applications.